1. Field of the Invention
The invention relates to an opposite rotating motor and an opposite rotating fan, and in particular to a three-phase opposite rotating motor having a single stator and two rotors and a three-phase opposite rotating fan having thereof.
2. Description of the Related Art
A conventional motor used in an axial fan comprises a single stator and a single rotor. To increase the output airflow or to prevent the primary fan from malfunctioning, it is essential that an auxiliary fan be disposed in series next to the primary fan. In fact, the primary and auxiliary fans are two independent fans, i.e. each fan has its own power supply system. However, these fans occupy a larger space and require a lengthy installation process, and the auxiliary fan increases the manufacturing cost. Further, it is possible that the resistance between the primary and auxiliary fans may be increased, so that the airflow cannot be efficiently raised because they are independent from each other. Thus, a motor with a single stator and two rotors is provided.
In FIG. 1, a motor M, a single-phase and core type motor, has a top rotor 11, a bottom rotor 12 and a middle stator 13 disposed between the top and bottom rotors 11, 12. A plurality of magnets serving as poles are circumferentially embedded in the top and bottom rotors 11, respectively. The number of magnets of the top rotor 11 is equal to that of the bottom rotor 12. The number of electrodes disposed in the middle stator 13 is equal to that of magnets of the top and bottom rotors 11, 12. Each electrode is formed by stacked thin silicon steel wound by exciting solenoids outwardly. The motor M has three Hall elements H1, H2 and H3 to detect a magnetic flux from the top rotor 11 so that the detected magnetic flux can be converted into a voltage signal to cause the middle rotor 13 to perform phase switching.
The electrodes and the Hall elements H1, H2 and H3, however, are difficult to install in and above the middle rotor 13, respectively. Furthermore, attractive force generated between the bottom rotors 11, the middle stator 13 and the bottom rotor 12 causes a large the ripple effect in rotation, resulting in a high start-up voltage and an unstable control of the magnetic declination. Thus, the rotational direction of the bottom rotors 11 can not rotate to be opposite the rotational direction of the bottom rotor 12, i.e., the top and bottom rotors 11 and 12 may rotate in the same direction.